The objective of this proposal is to test the hypotheses that a CO2 laser can be safely delivered to the distal airways and that sufficient energy for therapy could be directed at desired locations in the airway. The ND: YAG laser is the current laser of choice for laser bronchoscopy. Its deep tissue penetration (up to 10 mm) is beneficial for coagulation but presents significant risk of airway perforation. Accordingly, the ND: YAG laser can be only used in a limited fraction of affected patients and only by very few experienced professionals. CO2 lasers possess highly desirable cutting and ablation properties including very high precision and ultra-low depth of penetration. CO2 lasers cannot currently be used for tracheo-bronchial applications due to the lack of an adequate fiber delivery system. OmniGuide Communications (OGCI) has developed a new approach for the fabrication of photonic bandgap fibers, resulting in fibers for CO2 delivery, which are flexible and small enough to fit through working channels of commercially available flexible bronchoscopes. Preliminary trials have shown that these fibers can deliver sufficient laser energy for ablation and coagulation through flexible bronchoscopes under typical bending conditions. Introduction of CO2 lasers to the treatment of airway obstruction will provide a new debulking tool, potentially reducing surgical risk and improving clinical outcome. The proposed effort will include the following specific aims: Specific Aim 1: To develop a side-firing CO2 laser carrying fiber assembly. Specific Aim 2: To determine the optimal dose for lung tumor destruction. Specific Aim 3: To test the safety and feasibility of CO2 laser energy transmission through a flexible bronchoscope into live animal airways. The final goal of this Project is to demonstrate feasibility and generate sufficient safety data to enable human clinical trials in Phase II. [unreadable] [unreadable]